The present invention relates to fluid flow control devices. The invention is particularly useful as a valve for controlling the flow of water or other liquid, and is therefore described below with respect to this application.
Whenever it is desired to permit fluid flow only in one direction, a check valve may be used; and whenever it is desired to reduce the pressure between the inlet and outlet, a pressure-reducer or expansion valve may be used. Many different types of check valves and pressure-reducer valves have been developed and are commercially available.